Chilling requirement for deciduous fruits under climate change in Egypt

Many fruit trees require cold temperatures in winter to break dormancy. Quantifying this chilling requirement and selecting appropriate cultivars for the climate of a growing region is crucial for successful cultivation of such crops. It was tested that the hypothesis global warming is causing accumulated winter chill to decrease across the fruit growing regions in Egypt. The detection of potential trends in accumulated winter chill (between 0 and 10 °C) was determined using climate datasets. Several models exist can quantify winter chill, and each growing region uses a model that has been shown to perform well under local climatic conditions. The sensitivity of chilling model to projected climatic change was tested likely to affect fruit production in the near future. Fourteen sites in Egypt based on hourly and daily temperature records, winter chill was modeled for three past temperature (1970, 1990 and 2009), and temperatures in 2050 derived from three IPCC-AR4 General Circulation Models (CSIRO, HadCM3 and MIROC) for A2 greenhouse gas emissions scenario. Mean winter chill for each site and year was calculated using the Chilling Hours. Chilling models predicted substantial decreases in winter chill at all sites, but the extent of these decreases varied depending on sits. The results suggest that chilling hours during the winter season could decrease substantially under the under warming scenarios provided by current GCMs. In all scenarios, winter chill in Egypt declined substantially over time. The MIROC GCM projected the greatest warming and thus the greatest decreases in winter chill, followed by the HadCM3 and CSIRO GCMs. Averaging over all three General Circulation Models annual winter chill loss by 2050 compared to 1970 would amount to moderate 17.7 % and 22.6 %, if the climate simulated by the MIROC GCM which consistently caused the greatest decline in winter chill, turns out to be accurate. Research efforts are needed to identify the most appropriate chilling model for preparing fruit growers for the imminent effects of climate change.